An Integrated Transient and Steady-State Adhesive Wear Model

The integrated adhesive wear model tokes into account both the transient wear and the steady-state wear in wear testing. The transient wear volume is described by an exponential equation while the steady-state wear by a revised Archard's equation. In this study, the integrated wear model was used to analyze experimental wear data obtained previously for an A6061-T6 alloy and MMC-D, an aluminium alloy matrix composite containing 20% spherical alumina particles. Two loads of 7.5 kgf and 10.0 kgf, and a speed of 4.58ms^?1 were used in conducting the experiments. Both the standard wear coefficient and the net steady-state wear coefficient values for both types of materials were determined. On the average, the average standard steady-state wear coefficient, as compared with the net steady-state wear coefficient, was about 52% higher for MMC-D and 246% higher for A6061-T6. A higher load was found to have the effect of increasing the wear coefficient values.     

A Wear Model of Plane Sliding Pairs Based on Fatigue Contact Analysis of Asperities

Wear modeling is essential to predict and improve wear resistance of machine parts. This article presents a fatigue wear model of plane sliding pairs under dry friction. The wear model is constructed through developing a dynamic contact model of surfaces and proposing a mean fatigue damage constant of asperities. It is simpler and more practical than existing fatigue wear models because it describes the quantitative relationship between the wear behaviors of the plane sliding pairs and the main factors including the load and sliding speed, material property, friction property, and surface topography of the pairs. Furthermore, the wear model can predict the wear of each component of the sliding pairs. Reasonability and applicability of the wear model are validated via pin-on-disc wear tests. The wear model is applicable to predict the wear of the plane sliding pairs, which is characterized by friction fatigue of contact surfaces. The wear model can also be used to guide the tribological design of sliding pairs in machinery.     

Prediction of Steady-State Wear Coefficients in Adhesive Wear

With an integrated adhesive wear model, Yang's second wear coefficient equation was previously found suitable for modeling the standard wear coefficients for both the transient wear and the steady-state wear of MMC-A, MMC-B, and MMC-C, which are aluminium-based matrix composites containing 10%, 15%, and 20% alumina particles, respectively. In this study, Yang's third wear coefficient equation was used to predict the standard wear coefficient and the net steady-state wear coefficient, respectively, for MMC-D, an aluminium alloy matrix composite containing 20% spherical alumina particles, and an aluminium alloy A6061-T6. As compared with the wear data obtained previously, the average deviations were found to be about 23% and 15%, respectively, for the predicted standard wear coefficients and about 20% and 65% for the predicted net steady-state wear coefficients for the two materials respectively. The high deviation of about 65% obtained for the aluminium alloy was due to the very low wear rate obtained during wear testing with a long sliding distance, with the presence of powdery debris.     

A Study of Wear Chemistry and Contact Temperature Using a Microsample Four-Ball Wear Test

This study demonstrates that insight into the tribological reactions taking place in mixed and boundary lubrication can be provided by combining microsample four-ball wear tests with chemical analysis using gel permeation chromatography (GPC) as the principal analytical tool. At the end of the microsample four-ball wear test the lubricant turns into a grease-like mixture preventing the liquid lubricant from recirculating into the wear track and thus causing failure. Analyses of the various lubricant samples after their failure in the microsample test all show a relatively small amount of insoluble deposits and a large quantity of unreacted fresh lubricant. Virtually no intermediate reaction products were found. Combining this information with lubricant stability and the fact that a large quantity of lubricant flowed through the sliding junction while only a small portion was oxidized suggests that two very different thermal environments exist in the concentrated contact. The insoluble deposits are typical of thermal oxidative reactions that require temperatures of400°C or above. The unreacted lubricant found at failure indicates that this portion of the lubricant sample was maintained at temperatures of 150°C or below. The formation of grease-like mixture with as little as four percent reacted material indicates the remaining liquid lubricant and its insoluble reaction deposits were well mixed throughout the test. These findings suggest that the hot zones causing severe lubricant degradation are in the immediate vicinity of the asperity-asperity contacts while the low temperature zone - the valleys between asperities which are in the majority - are much cooler.     

销盘滑动磨损试验的仿真建模研究

以销盘滑动磨损为研究对象,建立了表面微凸体接触特性的物理模型和数学模型,由微凸体接触产生的磨屑推导出销盘滑动磨损仿真模型.采用有限元分析软件ANSYS对半球形微凸体接触应力和变形进行了仿真计算,并用销盘滑动磨损试验数据给予验证,证明了所建立的仿真模型是可行的.研究表明,利用ANSYS求解摩擦学接触问题是准确可靠的,建立正确的磨损仿真模型并辅以参数化设计方法是解决摩擦学仿真问题非常有效的方法.     

Improved Elastic Contact Model Accounting for Asperity and Bulk Substrate Deformation

An improved elastic contact model for a single asperity system is proposed accounting for both the effects of bulk substrate and asperity deformations. The asperity contact stiffness is based on the Hertzian solution for spherical contact, and the bulk substrate stiffness on the solution of Hertzian pressure on a circular region of the elastic half-space. Depending on the magnitude of the applied load, as well as the geometrical and physical properties of the asperity and bulk materials, the bulk substrate could have considerable contribution to the overall contact stiffness. The proposed single asperity model is generalized using two parameters based on physical and geometrical properties, and is also verified using finite element analysis. A parametric study for a practical range of geometric and physical parameters is performed using finite element analysis to determine the range of validity of the proposed model and also to compare it with the Hertz contact model. The single asperity model is extended to rough surfaces in contact and the contact stiffness from the proposed model and the simpler Greenwood–Williamson asperity model are compared to experimental measurements.     

Study of the Influence of Contact Geometry and Contact Pressure on Sliding Distance to Galling in the Slider-on-Flat-Surface Wear Tester

One of the major causes of tool failure in sheet metal forming is wear in the form of galling. Galling is gradual buildup of adhered sheet material on the tool and leads to unacceptable scratches on the sheet surface and to components that fail to meet tolerances. Because it is difficult to reproduce operational and interactional conditions in laboratory test equipments it is hard to test, model, and predict galling initiation.

Here the authors examine how changes from elliptical to line contact geometry influenced galling initiation under dry sliding by using a slider-on-flat surface (SOFS) wear tester. A micro clean tool steel was tested against ferritic low-strength and martensitic high-strength steel sheets.

The sliding distance to galling initiation was extracted from friction data and verified by scanning electron microscopy (SEM) observations. The presence of adhesive wear on worn tools after completed tests was used as a criterion. Experimental results showed that the elliptical contact causes galling quicker than the line contact.

Applicability of experimental results depends on the relevance of test conditions, so contact pressures calculated for the described tests were compared to calculated contact pressures in a semi-industrial U-bending test and to literature data relevant to industrial applications. Good agreement between values observed for SOFS and for most selected industrial applications was found, which assume that contact pressures typical for most common industrial applications can be successfully simulated by selection of tool geometry and normal load in the SOFS tester.     

Tribological Characteristics of Sustainable Fiber-Reinforced Thermoplastic Composites under Wet Adhesive Wear

The friction and specific wear rate of sustainable kenaf fiber–reinforced polyurethane composites were investigated against stainless steel counterface and under wet contact conditions. The new composites were evaluated at different applied loads (50–80 N), sliding distances (up to 2.7 km), and fiber mat orientations. Scanning electron microscopy (SEM) was used to observe the damage features on the worn surfaces. The results revealed that sustainable kenaf fibers assisted in enhancing the wear and frictional performance of the polyurethane thermoplastic composite by about 59 and 90%, respectively. Operating parameters and mat orientation controlled the wear and the frictional behavior of the composite. Better wear performance was exhibited at high loads and when the fiber mats were oriented perpendicularly to the sliding direction. Observations of the worn surfaces revealed different features of damage such as microcracks, fiber tearing, fiber detachment, and delamination. However, there was no trace of fiber pull-out in any of the tested conditions.     

Wear Behavior of Aluminum Alloys at Slow Sliding Speeds

The investigated slow sliding speeds presented in this work enable the understanding of the wear behavior on aluminum alloys and could possibly facilitate the completion of the previously proposed wear mechanism map for aluminum at this slow sliding speed range. Dry sliding block-on-ring wear tests were carried out on aluminum alloys, AA5754 (Al-Mg), AA6082 (Al-Mg-Si), and AA7075 (Al-Zn-Cu), at a very slow sliding speed range (<0.01 m/s). A bearing steel ring of AISI 52100 was used as the counterbody. Tests were performed at varying contact pressures, 20, 100, and 140 MPa, and sliding speeds ranging from 0.001 to 1.5 m/s. The wear tracks and debris collected were examined by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD), with the aim of analyzing their morphology and composition. At relatively slow sliding speeds (>0.01 m/s), the specimens exhibited a wear process placed at the mild wear regime, characterized by oxidation and delamination mechanisms of both the aluminum specimen and the steel ring. However, at very slow speed range (<0.01 m/s), an increase in the wear rate and the friction coefficient is observed for all of the aluminum alloys, thus suggesting that an alternative wear mechanism could be taking place.     

铸锡青铜与巴氏合金抗粘附磨损的实验研究

基于对磨损影响因素拓展分析的所悟，并依据“相容性”理论，率先尝试改铸锡青铜注塑机拉杆衬套为钢背内衬巴氏合金衬套，在SZ－4000型塑料注射成型机上进行了500h工况对比实验，实验结果表明，解决磨损问题不能仅局限在对抗磨材料的研制与单纯提高材料的硬度；提出了摩擦副偶件间材质硬度差值的大小及表面粗糙度的匹配也是问题关键的观点。     

Identification of wear process parameters in reciprocating ball-on-disc tests

Wear test results are presented for a spherical indenter in reciprocal motion interacting with soft (aluminium alloy) and hard (construction steel) substrates. The aim of this paper is to provide evidence of the evolution of the contact zone, specification of wear scar depth and surface roughness in the contact zone. Numerical analysis of the interaction of the sliding sphere with the wear track provided contact zone dimensions, although these differed from the experimental data. The incremental wear factor is also introduced in the paper, while the formulae for the wear volume of the sphere recommended by ASTM have been improved.     

A predictive modeling scheme for wear in tribometers

Study of wear in complex micro-mechanical components is often accomplished experimentally using a pin-on-disc and twin-disc tribometer. The present paper proposes an approach that involves a computationally efficient incremental implementation of Archard's wear model on the global scale for modeling sliding and slipping wear in such experiments. It will be shown that this fast simplistic numerical tool can be used to identify the wear coefficient from pin-on-disc experimental data and also predict the wear depths within a limited range of parameter variation. Furthermore, it will also be used to study the effect of introducing friction coefficient into the wear model and also to model water lubricated experiments. A similar tool is presented to model wear due to a defined slip in a twin-disc tribometer. The resulting wear depths from this tool is verified using experimental data and two different finite element based numerical tools namely, the Wear-Processor, which is a FE post-processor, and a user-defined subroutine UMESHMOTION in the commercial FE package ABAQUS. It will be shown that the latter two tools have the potential for use in predicting wear and the effective life span of any general tribosystem using the identified wear coefficient from relevant tribometry data.     

基于齿轮箱整体模型的齿轮有限元接触分析

提出了一种应用叠加原理计算齿轮箱整体变形的方法,包括箱体、轴承、传动轴和齿轮的变形。重点阐述了利用ANSYS刚体耦合功能生成齿轮箱体柔度矩阵,建立柔度矩阵、载荷向量、变形向量三者关系方程,从而计算箱体变形的方法。以风力发电增速器齿轮箱为例,分析齿轮箱整体变形对支点反力和齿面接触应力及齿根弯曲应力的影响。     

Adhesive Wear Performance of T-OPRP and UT-OPRP Composites

In the current work, the effects of treating the oil palm fibres on the tribological performance of polyester composite were studied against polished stainless steel counterface using Block-on-Ring (BOR) technique under dry contact condition. Wear and friction characteristics of treated and untreated oil palm fibre reinforced polyester (T-OPRP and UT-OPRP) composites were evaluated at different sliding distances (0.85–5 km), sliding velocities (1.7–3.9 m/s) and applied loads (30–100 N). SEM observations were performed on the worn surfaces of the composites to examine the damage features. Specific wear rate (Ws), friction coefficient and interface temperature results were presented against the operating parameters. The results revealed that test parameters significantly influenced the wear performance of the composites. Both treated and untreated oil palm fibres enhanced the wear and frictional performance of polyester composites. T-OPRP showed less Ws by about 11% compared to UT-OPRP. This was due to the better interfacial adhesion offered by the treated fibres. The SEM observation made on UT-OPRP worn surface showed debonding and bending of fibres, and fragmentation and deformation on the resinous regions. Meanwhile, T-OPRP composite showed less damages compared to UT-OPRP, where no sign of fibres debonding was observed.     

不同摩擦副中Si3N4陶瓷摩擦磨损特性研究

奥氏体不锈钢1Cr18Ni9Ti是难切削材料之一。本研究采用一种销盘试验机,模似陶瓷刀具实际切削加工时使用状况,考察了Si_3N_4/不锈钢摩擦副的摩擦学性能,并着重考察了与不锈钢对磨时Si_3N_4陶瓷的磨损特性。作为比较,对Si_3N_4/45号钢摩擦副的摩擦磨损性能也进行了较为详细的考察。试验结果表明,相同试验条件下,Si_3N_4/不锈钢中Si_3N_4,陶瓷的磨损率比Si_3N_4/45~#钢摩擦副中Si_3N_4的磨损率约大2个数量级。润滑剂对两种摩擦副摩擦磨损性能的影响也有很大差别。借助扫描电镜,X光电子能谱,俄歇电子能谱等多种分析手段对Si_3N_4陶瓷的磨损机理进行了分析,并对两种摩擦副中Si_3N_4磨损率的差别作了讨论。     

Acoustic Emission and Its Relationship with Friction and Wear for Sliding Contact

Further investigation of the relationships between friction and wear properties and the characteristics of acoustic emission was conducted in the case of dry and grease-lubricated sliding contact using a ball-on-cylinder testing apparatus. The effect of contamination simulated by the inclusion of glass bead particles was also explored. Experiments were performed at sliding speeds ranging from 0.09 m/s to 1.47 m/s, while maintaining a fixed load and duration. As a first observation and contrary to what could be expected, the higher speed did not contribute to the decrease in friction interpreted by a worsening of the starved regime that had a consequence of increasing wear. However, the results revealed a good correlation between the friction coefficient and acoustic emission (AE) rms voltage for dry sliding. Such a relationship may allow the prediction of a reasonable friction coefficient μ from an AE signal. It was also determined that the friction work correlated well with the corresponding integrated AE voltage over time, intRMS. The detection of the sliding speed threshold beyond which accelerated wear would occur was possible from the intRMS variation. Proportionality between the theoretically determined grease film thickness and the intRMS was observed.     

超高速滑动电接触CuCrZr合金轨道表面磨损机制及电接触性能

电磁轨道发射具有典型超高速滑动电接触特性（出口速度大于等于2 000 m/s）,电磁轨道表面会发生磨损。为研究轨道表面磨损状态与接触电阻之间关系,通过开展电磁轨道发射试验,研究发射后的CuCrZr轨道表面沉积层的形成与磨损机制,揭示枢轨间静态接触电阻的演变规律,总结沉积层的形成与接触电阻的关联关系。结果表明：沿着发射方向,轨道表面沉积层覆盖面积逐渐增大,沉积层的形成机制由摩擦材料转移变为电枢表面熔化飞溅,表面磨损特征由机械磨损向电气磨损转变;由于轨道不同位置沉积层形成原因不同,导致表面粗糙度分布不一致,枢轨间静态接触电阻随接触沉积层形貌特征改变呈现上升、下降及波动3个变化阶段;并且枢轨间静态接触电阻随着接触压力的增大而减小。研究成果对电磁轨道发射装备的研究及发射动力学研究具有理论价值。     

Wear of Silicon Carbide in Sliding Contact with Lubricated Thin-Film Rigid Disk

Silicon carbide (SiC) is a potential ceramic material for recording heads, yet its tribological performance against lubricated thin-film rigid disks is not fully known. Square pins with a 100 mm radius spherical surface were made from hot pressed SiC, chemical vapor deposited (CVD) SiC, and Al₂O₃TiC, and tested with lubricated thin-film disks. The pin-on-disk tests showed that the region of contact on the spherical surface of the SiC and CVD-SiC pins wears away to form a circular wear plateau with smears in and around the plateau. The wear plateau is formed rapidly in the first 1000 drag revolutions and then very gradually grows in size with further revolutions. Analysis of the smears showed that a large fraction of the smears contained SiO₂ which had been oxidized from SiC due to high temperatures generated at the pin surface in contact with the disk. In contrast, tests with Al₂O₃. TiC pins did not show any formation of a wear plateau on the pins.